1. Field of the Invention
The present invention relates to a color liquid crystal electro-optical device used for personal computers, pocket television and the like.
2. The Prior Art
FIG. 5 is a sectional view of a conventional color liquid crystal electro-optical device. FIGS. 5(a) and (b) are sectional views shown the device viewed from angles rotated at an angle of 90.degree. respectively. The structure of this color liquid crystal electro-optical device is as follows. A transparent electrode 53 patterned is disposed on the surface of a glass substrate 51. The color filters 56R, 56G, 56B are in order provided the transparent electrodes 53. A black matrix 57 is provided between the gap of the color filters.
Furthermore, an overcoat layer 58 is provided on the color filters and the black matrix. A patterned transparent electrode 54 is provided on the surface of the overcoat layer 58.
Another transparent substrate 52 faces the color filter substrate 51. A patterned transparent electrode 55 is provided on the surface of the transparent substrate 52. The two substrates are adhered to each other with a sealing material 59 to define and a space to enclose liquid crystal 60 between the two substrates.
Basic structure of a liquid crystal cell of a color liquid crystal electro-optical device is explained above. As a general structure, a color liquid crystal electro-optical device has polarizing plates adhered to each exterior side the said color filter substrate and the transparent substrate, a power supply unit to drive the liquid crystal, a controller unit and a backlight unit.
The transparent electrode pattern 53 is provided under the color filters 56R, 56G and 56B of said color filter substrate, and the electrode pattern 53 is required when the color filters are formed by a paticular color filter manufacturing method, namely, the high polymer electro-deposition method or the micell electrolytic method. In using color filters made by the dyeing method, the printing method or the pigment distribution method, the transparent electrode pattern 53 is unnecessary and not provided.
Recently, the STN (Super Twisted Nomatic) mode having excellent electro-optical properties is in most cases applied to the liquid crystal cell of the color liquid crystal electro-optical device. Especially, in the majority of the color liquid crystal electro-optical devices for personal computers, the STN mode is adopted because of its large size and high resolution.
One of the most important requirements for the STN mode liquid crystal cell is the uniformity of the cell gap.
The cell gap is the thickness of the liquid crystal 60 sealed between the substrates in FIG. 5. The cell gap between the color filter substrate 51 and the opposing substrate 52 is controlled carefully by the sealing material 59 and spherical fine powder called a gap control material.
The uniformity required for the cell gap is below .+-.0.1 .mu.m. If the uniformity of the cell gap becomes over .+-.0.1 .mu.m, this non-uniformity of the color liquid crystal electro-optical device usually causes deterioration of the visible properties, and results in problems such as irregular tone and low contrast.
Generally, each transparent electrode 53, 54 and 55 provided in the liquid crystal cell of the color liquid crystal electro-optical device shown in FIG. 5 has a film thickness ranging from 0.10 .mu.m to 0.30 .mu.m. Particularly, the film thickness of the transparent electrodes 54 and 55, because of lowering the value of their resistance, tend to get thick, so the film thickness is over 0.2 .mu.m at present.
However, in the structure of the conventional liquid crystal cell, at the sealing portion where the sealing material 59, which is important to control the cell gap, is provided, in some portion the patterned transparent electrodes 53, 54 and 55 are provided, but in other portions those are not provided. This causes a serious defect in regards of uniformity of the cell gap.